Shooter’s chilling final Facebook post

IN an eerie final Facebook post, the former US Marine who allegedly massacred 12 people in a California bar ranted about mass shootings and the "hopes and prayers" commonly offered to victims after them, according to a report.

"I hope they call me insane … (laughing emojis) wouldn't that just be a big ball of irony?" Ian David Long, 28, wrote around the time of the attack, police officials told CNN.

"Yeah … I'm insane, but the only thing you people do after these shootings is 'hopes and prayers'. or 'keep you in my thoughts' … every time … and wonder why these keep happening …"

Police told the outlet the post was made by Long, but the shooter's Facebook account or other posts haven't been previously reported, reports the New York Post.

On Wednesday night local time, Long stormed into the Borderline Bar & Grill in Thousand Oaks, about 65 kilometres north of Los Angeles, and unleashed a hail of bullets before turning the gun on himself.

Long killed 12 people, including a policeman who had rushed in to help.

Ian Long reportedly had a history of mental health issues. Picture: Facebook

Ian Long was a former Marine. Picture: Facebook

It comes as one of Long's high school PE teachers recalled him lunging at her and shaking with rage.

Dominique Colell told the Los Angeles Times that Long "lunged" at her in 2008 when he was a student at Newbury Park High School.

Ms Colell, then 28, was the girls athletics coach and also disciplined the boys team.

"He started to grab at me," Ms Colell told the paper.

"He reached around and with one arm, groped my stomach. He grabbed my butt with the other arm."

Ian Long’s high school sports teacher school sports teacher Dominique Colell (right) has described her former student as volatile. Picture: Facebook/CBS

The incident erupted when the coach found a mobile phone and was trying to figure out who owned it.

When Long saw Ms Colell with the device, he rushed over, yelling expletives and demanding that she hand it over.

But she refused, telling him she needed to make sure it was his, by calling the number listed under "Mum."